Results 1 - 10 of 20
Results 1 - 10 of 20. Search took: 0.014 seconds
|Sort by: date | relevance|
[en] The image-forming factors of X-ray generators and X-ray exposure systems must have an optimum adaptation to the patient to be examined. Meeting this requirement, apart from the necessary standardization of the cassettes, the film / intensifying screen combination and the film developers, is the precondition for a successful working with the X-ray exposure system. Recent developments in this field show a trend towards the automatic and patient-specific choise of the measuring field and the density (blackening) in X-ray exposure systems. Besides, they confirm the tendency to determine optimum image formation factors on the basis of objective physical measuring processes. (author)
[en] Corrosion of reactor material during oxidation of hazardous organic waste containing chloride proceeds very fast and constitutes one major problem in SCWO applications. The following Ni-base alloys were tested within the framework of the experimental program: Inconel 625 and 686, Hastelloy C-276, Nicrofer 5923 and 6025, and Haynes alloy 214. Test tubes were fabricated from these materials and exposed to SCWO conditions, without organics, at temperatures up to 600 C and pressures up to 34 MPa. Higher concentrated HCl solutions or the combination of oxygen and HCl cause strong surface destruction. The corrosion measured was higher at lower temperatures and at higher pressures, if all other conditions remained constant. The most severe corrosion--general corrosion with SCC and pitting--appeared at temperatures near the critical temperature, i.e., in the preheater and cooling sections of the test tubes. The corrosion products were insoluble in supercritical water and formed thick layers in the supercritical part of the reactor. Under these layers only minor corrosion occurred
[en] Aim: To judge the possibilities of detection of orbital foreign bodies in multidetector CT (MDCT) with a focus on glass slivers. Materials and Methods: Experimental systematic measuring of Hounsfield Units (HU) of 20 different materials, containing 16 different types of glass with 4 different types of ophthalmic lenses among them. The measurements were performed using a standardized protocol with an orbita phantom being scanned with 16-slice MDCT. Using the resulting density values, the smallest detectable volume was calculated. Using this data we produced slivers of 5 different glass types in the sub-millimeter range and calculated their volume. Those micro-slivers underwent another CT scan using the same protocol as mentioned above to experimentally discern and confirm the detection limit for micro-slivers made of different materials. Results: Glass has comparatively high density values of at least 2000 HU. The density of glasses with strong refraction is significantly higher and reaches up to 12 400 HU. We calculated a minimum detectable volume of 0.07 mm3 for glass with a density of 2000 HU. Only glass slivers with a density higher than 8300 HU were experimentally detectable in the sub-millimeter range up to a volume as small as 0.01 mm3. Less dense glass slivers could not be seen, even though their volume was above the theoretically calculated threshold for detection. Conclusion: Due to its high density of at least 2000 HU, glass is usually easily recognizable as an orbital foreign body. The detection threshold depends on the object's density and size and can be as low as 0.01 mm3 in the case of glass with strong refraction and thus high density. The detection of glass as an orbital foreign body seems to be secure for slivers with a volume of at least 0.2 mm3 for all types of glass. (orig.)
[en] 151Eu Moessbauer studies of La1.83-xEu0.17SrxCuO4 for 0≤x≤0.26 exhibit a quadrupole interaction at the Eu site whose magnitude eQVzz strongly depends on both the Sr content x and the temperature T. For a fixed temperature, a linear relationship is obtained between the quadrupole interaction and the averaged CuO6 octahedra tilting angle determined from diffraction studies. The unusually large temperature dependence of eQVzz strongly indicates a temperature dependence of the local structure. In contrast to recent studies of the local structure La2CuO4-type superconductors by means of x-ray-absorption and neutron-scattering techniques, our data give strong evidence that the local octahedra tilting in La1.83-xEu0.17SrxCuO4 corresponds well to the average tilting obtained by diffraction techniques. copyright 1996 The American Physical Society
[en] We conducted a prospective randomized study of the benefit of adjuvant radiation therapy delivered by the brachytherapy technique in 117 adult patients who had soft-tissue sarcoma that was on an extremity or superficially localized to the trunk. A significant decrease in local recurrence was demonstrated in the patients receiving brachytherapy. The benefit did not appear to be due to any maldistribution in the known prognostic factors of size, site, depth, presentation with recurrence, or histologic grade. The decrease in local recurrence appears to be due to the decreased local recurrence in high-grade sarcomas. Survival differences were not identified, and accrual and follow-up were continued
[en] The dimpling in the CuO2 planes of overdoped Y1-yCayBa2Cu3O6.96-6.98, (y=0.02-0.2) has been measured by x-ray absorption-fine-structure spectroscopy (Y-K EXAFS). A step-like decrease around 12% Ca indicates a percolation threshold for distorted sites of 5 cells, and thus phase segregation. We conclude the charge carriers added by substitution of Y3+ by Ca2+ to be trapped at the Ca sites and their nn environment
[en] InxGa1-xN alloys have attracted considerable interest due to their wide range of applications in optoelectronic devices, e.g. blue and green lasers. Although the quality of In-rich epitaxial layers has improved in recent years, there is still not much known about the atomic structure of InxGa1-xN surfaces. The influence of the surface structure on the growth of InxGa1-xN layers and on the interface formation in hetero-structures remains unclear. Here we present our results on InxGa1-xN surface properties after deoxidation under ultra high vacuum (UHV) conditions. Auger Electron Spectroscopy measurements of the chemical surface composition confirm residual contaminations such as carbon and oxygen even after annealing up to 600 C. Further annealing at higher temperatures leads to a strong reduction of carbon and oxygen and LEED reveals a (3 x 3)-surface periodicity. Scanning tunnelling microscopy (STM) measurements on such prepared surfaces show atomically flat terraces and both more metallic-like and more semi-conducting areas. Based on these results surface structure models are discussed
[en] Surfaces of the InGaN alloy system are hardly understood in terms of their atomic structure. In order to reveal the principal mechanisms for the formation of surface reconstructions the preparation of such surfaces for measurements in ultra-high vacuum (UHV) is crucial. The preparation and surface structure of high quality group-III-polar (0001) InGaN layers grown by metal-organic vapor phase epitaxy have been investigated. We show that different InGaN surface reconstructions such as (1 x 1), (1+1/6), (2 x 2) and (√(3) x √(3))R30 circle can be obtained by annealing at various temperatures under ultra-high vacuum and nitrogen-rich conditions as observed by low energy electron diffraction. Depending on the annealing temperature and nitrogen supply these surfaces exhibit significant differences in stoichiometry and morphology as determined by Auger electron spectroscopy and atomic force microscopy measurements. We show that the (2 x 2) and (√(3) x √(3))R30 circle are explained by indium-adatoms and a related In depletion in the first group-III layer underneath whereas the (1+1/6) exhibits a discommensurate overlayer of group-III-atoms. Strain-relaxation is suggested to explain this structure formation.
[en] Nanopore force spectroscopy is used to study the unzipping kinetics of two DNA hairpin molecules with a 12 base pair long stem containing two contiguous stretches of six GC and six AT base pairs in interchanged order. Even though the thermodynamic stabilities of the two structures are nearly the same, they differ greatly in their unzipping kinetics. When the GC segment has to be broken before the AT segment, the unfolding rate is orders of magnitude smaller than in the opposite case. We also investigated hairpins with stem regions consisting only of AT or GC base pairs. The pure AT hairpins translocate much faster than the other hairpins, whereas the pure GC hairpins translocate on similar timescales to the hairpins with only an initial GC segment. For each hairpin, nanopore force spectroscopy is performed for different loading rates and the resulting unzipping distributions are mathematically transformed to a master curve that yields the unfolding rate as a function of applied voltage. This is compared with a stochastic model of the unfolding process for the two sequences for different voltages. The results can be rationalized in terms of the different natures of the free energy landscapes for the unfolding process.